1. Mix the flour, yeast, sugar, cardamom and ½ tsp salt in a large bowl. Melt the butter in a small pan, add the milk and warm to room temperature. Beat in the egg and vanilla paste with a fork. Stir this into the flour mix to make a rough, sticky dough then set aside for 10 minutes.
2. Knead the dough on a floured surface for 5-10 minutes until smooth and elastic, then leave to rise in an oiled bowl covered loosely with oiled clingfilm for 1 hour, or until doubled in size.
3. Meanwhile, prepare the filling. Chop the chocolate and mango into 1cm chunks. Mix the cardamom with the sugar. Line a large baking sheet with baking parchment.
4. Flour the work surface generously, then turn the dough out from the bowl. Dust it with more flour then, without any kneading, roll the dough to a 30 x 60cm rectangle. Scatter with the fruit, chocolate and cardamom sugar, then roll up into a long sausage. Flatten a little to seal, then cut in half lengthways, keeping one end joined. Twist the 2 ropes of dough together, lift onto the baking sheet then press the ends together to make a ring. If you lose any chocolate or mango along the way, just poke it back in. Cover loosely again and leave to prove in a warm place for 30 minutes. Preheat the oven to 200°C, gas mark 6.
5. Bake the bread for 25-30 minutes or until golden and risen. It will sound hollow when tapped underneath. Warm the jam with a splash of water, then brush it over the warm bread to glaze. Scatter with pistachios and slice to serve.